Proper connectivity of the central nervous system allows for communication between hemispheres necessary for such diverse functions as locomotion and linguistic processing. A clear understanding of how an individual axon growth cone makes a guidance decision during development is necessary to learn how reproducible connectivity patterns are accomplished in normal development. Knowledge as to how axon guidance receptors convert extracellular cues into a guidance choice will be essential to serve the long-term goal of guiding rewiring in developmental disease, neurodegenerative disease or injury states. This proposal is designed to provide mechanistic insight into the how the regulation of signaling of one axon guidance receptor, Roundabout (Robo) affects its repulsive guidance instruction. Determining whether and how the spatiotemporal profile of activated Robo affects growth cone guidance is a largely unexplored topic and may provide insight into general mechanisms of guidance receptor regulation. The proposed experiments use Drosophila genetics, biochemistry, and cell culture approaches to test the hypothesis that ligand-dependent internalization of Robo, by proteolysis and endocytosis, regulates the spatiotemporal dynamics of signaling within a growth cone during repulsive guidance. Knowledge of the mechanism by which an activated receptor informs wiring decisions will provide insight into optimal points of therapeutic intervention in developmental diseases of miswiring and repair following injury or neurodegenerative disorder.